Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant pressure

Takes place at constant entropy

Takes place at constant temperature

Involves no change in volume

2. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Less

Equally

3. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

Detect liquid in vapour

4. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 9

9: 1

1: 3

1: 1

5. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Freon

Brine

Ammonia

Carbon dioxide

6. The curved lines on a psychrometric chart indicates

Relative humidity

Wet bulb temperature

Dry bulb temperature

Dew point temperature

7. In a lithium bromide absorption refrigeration system

Lithium bromide is used as a refrigerant and water as an absorbent

None of these

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

8. Critical temperature is the temperature above which

A gas will immediately liquefy

Water will never evaporate

Water will evaporate

A gas will never liquefy

9. The value of C.O.P in vapour compression cycle is usually

Always more than unity

Any one of the above

Always less than unity

Equal to unity

10. Which of the following is not a desirable property of a refrigerant?

High risibility with oil

Good electrical conductor

Low boiling point

Large latent heat

Page 2 of 4

11. The minimum temperature to which water can be cooled in a cooling tower is

Dry bulb temperature of air

Wet bulb temperature of air

Dew point temperature of air

Ambient air temperature

12. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

4.33

3.33

1.33

2.33

13. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Positive

Negative

None of these

Zero

14. The operating pressure for refrigerating units using R-12 as a refrigerant is

15 bar

8 bar

2 bar

30 bar

15. In a refrigeration system, the expansion device is connected between the

Evaporator and compressor

Receiver and evaporator

Condenser and receiver

Compressor and condenser

16. The boiling point of ammonia is

-30°C

-77.7°C

-33.3°C

-10.5°C

17. Highest temperature encountered in refrigeration cycle should be

Much below critical temperature

Above critical temperature

Near critical temperature of refrigerant

At critical Temperature

18. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

19. The domestic refrigerator uses following type of compressor

Centrifugal

Piston type reciprocating

Axial

Miniature sealed unit

20. Cooling water is required for following equipment in ammonia absorption plant

Evaporator

Condenser, absorber and separator (rectifier)

Absorber

Condenser

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21. A bootstrap air cooling system has

One heat exchanger

Three heat exchangers

Four heat exchangers

Two heat exchangers

22. The bank of tubes at the back of domestic refrigerator is

Refrigerant cooling tubes

Evaporator tubes

Capillary tubes

Condenser tubes

23. The condition of refrigerant after passing through the condenser in a vapour compression system is

Saturated liquid

Superheated vapour

Wet vapour

Dry saturated vapour

24. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₂ - T₁)/T₁

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

25. The capillary tube, as an expansion device, is used in

Domestic refrigerators

Room air conditioners

Water coolers

All of these

26. A thermostatic expansion valve in a refrigeration system

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

None of the above

Is suitable only for constant load systems

27. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

5.12

2.15

28. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

29. For obtaining high COP, the pressure range of compressor should be

High

Optimum

Low

Any value

30. The freezing point of sulphur dioxide is

-75.2°C

-56.6°C

-77.7°C

-135.8°C

Page 4 of 4

31. Which of the following cycles uses air as the refrigerant?

Carnot

Ericson

Stirling

Bell Coleman

32. The vapour compression refrigerator employs the following cycle

Reversed Rankine

Reversed Carnot

Carnot

Rankine

33. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

34. Most thermostatic expansion valves are set for a superheat of

15°C

5°C

10°C

20°C

35. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

More for small capacity and less for high capacity

Less

36. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Sub-cooling or under-cooling

None of these

Super-cooling

Normal cooling

37. Freon group of refrigerants are

Inflammable

Nontoxic and non-inflammable

Toxic

Non-inflammable and toxic

38. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.6

0.376

0.4

0.67

39. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(D) Difference of (A) and (B)

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

40. Rating of a domestic refrigerator is of the order of

40 tons

0.1 ton

5 tons

10 tons

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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